The proposed work is a biochemical study of the endogenous carbohydrate binding proteins of Dictyostelium discoideum. These lectin-like molecules can be detected at the cell surface and are believed to play a direct role in intercellular cohesion during cell aggregation and subsequent morphogenesis. I have identified, in addition to the two previously described major CBP's (I and II), three distinct minor forms, which appear by peptide mapping studies to be variants of the major species. In addition, there are numerous tryptic peptides in common between CBP I and II, suggesting considerable sequence homology. I propose to determine whether the common and unique regions are segregated into domains within the CBP sequences, and to assess which regions correspond to the carbohydrate binding sites. Studies will also address, through the use of various labeling procedures and inhibitors, the possibility of post-translational modifications of the CBP's. Of particular interest is the structure of the apparently minor fraction of CBP which resides at the cell surface.